Basic construction of Slit lamp
The structure of the slit lamp is mainly composed of two parts, namely “Slit lamp” and “microscope”. In order to facilitate the slit light source from different angles of the eyes, and the microscope from different angles to observe the eyes, the requirements of the slit lamp and microscope on the mechanical have enough swing angle. The light source of the slit lamp requires that the crack edge must be very flat, the fissure must be clearly imaged on the vertical surface of the center of the left and right swing, and the focus of the microscope must also be focused on the vertical surface of the center.
The slit illumination light source must have: 1. The width of the fissure is adjustable within 0 to 14mm range; 2. The length of the fissure is adjustable in the range of 1 to 14mm (when the length width is 14mm in the light of a circular spot); 3. The direction of the fissure can be adjusted. That means that the fractured light source can be vertical or horizontal, and can be oblique; 4. Brightness of the light source is adjustable;
For digital photography fissure lamps, it should also have the brightness adjustable background lighting.
The microscope is three-dimensional binocular structure, must have: 1. Clear imaging; 2. Adjustable program lens focal length to accommodate the different eye diopter of the operator; 3. The distance between the two eyepiece can be adjusted to accommodate the pupil distance of different operators;
In addition to the mechanical structure of the above-mentioned swing function, but also have a three-dimensional adjustable mobile workbench; Jaw rack device can be fixed on the skull of the patient, jaw rack up and down can be adjusted to accommodate different patients with the skull length; solid light can avoid the patient’s eye unconscious rotation. 
When using diffuse illumination method, the use of set light, macroscopic magnification, can be a comprehensive observation of the cornea, iris, crystals.
When the direct focus illumination method is used, the bending degree and thickness of the cornea can be observed. There is no foreign body and corneal sediment (KP), as well as infiltration, ulcers and other pathological changes in the hierarchy and morphology; When focusing backward, the opacity of the crystals and 1/3 lesions in front of the vitreous are observed;
When using specular reflection irradiation, you can carefully observe the cornea and the lens before and after the subtle changes of the capsule, such as tear film on the shedding cells, corneal endothelial pattern, crystal before and after the capsule and adult nucleus of the pattern.
When using the rear reflective irradiation method, corneal epithelial or endothelial edema, corneal posterior composure, newborn blood vessels, slight scar, and Crystal hollow bubbles can be found.
When using the angle gong the Fate light illumination method, can discover the corneal extremely pale turbidity, such as thin shade, blisters, perforation, scar and so on.
When using indirect illumination method, we can observe the pupil sphincter, iris hemorrhage, iris vascular, corneal vascular nebula, etc. At the same time, the slit lamp microscope can attach front mirror, contact lens and three-face mirror, to inspect the peripheral retina, anterior chamber angle and the posterior vitreous body, with binocular observation can produce stereoscopic vision.
Therefore, through the slit lamp microscope examination, can identify wearing soft contact lens contraindication, for the wearer to choose appropriate soft contact lens.